Method for operating a wind energy plant

ABSTRACT

The present invention relates to a method for operating a wind turbine with a generator, drivable by a rotor, for supplying electrical power to an electrical load, in particular an electric grid. In order to compensate for fluctuations in the grid as far as possible, the system of the kind initially specified is developed in such a way that the power delivered to the load by the generator is regulated in response to a current outputted to the load.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for operating a wind turbinewith an electrical generator, drivable by a rotor, for supplyingelectrical power to an electrical load, in particular an electric grid.

The invention further relates to a wind turbine with a rotor and anelectrical generator coupled to the rotor for supplying electrical powerto an electrical load, in particular an electric grid.

2. Description of the Related Art

In known wind turbines for generating electrical energy from windenergy, the generator with the electrical load, often an electric grid,is operated in a grid-parallel mode. In other words, as soon as the windsupply is sufficient, the wind turbine will generate electrical energyand deliver it to the grid.

However, if a failure occurs in the grid, for example as a result of ashort circuit in the grid, wind turbines have hitherto been disconnectedfrom the grid and not reconnected to the grid until normal operatingconditions have been restored.

This means that, following such a grid failure, is no longer possible toprovide the rapid support for the grid that is particularly needed whenthere are large fluctuations in the voltage and/or power that isrequired.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide a controlsystem for one or more wind turbines that compensate as far as possiblefor fluctuations in the grid.

This object is achieved with a method of the kind initially specified,in which the power delivered to the load by the generator is regulatedin response to a current that is outputted to the load.

In a device of the kind initially specified, the object is achieved by acontrol device comprising a current sensor for measuring an electricalcurrent delivered to the load, such that the power delivered by thegenerator to the load can be controlled in response to the current thatis received by the current sensor.

In this way, the required power can be generated and delivered whenthere are fluctuations in the power requirements from the grid.

In order to avoid overload of parts of the wind turbine and/or the gridin the event of a grid failure, for example as a result of a shortcircuit in the grid, the wind turbine is controlled in such a way thatthe current delivered to the grid does not exceed a predefined value.

In a particularly preferred embodiment of the invention, the maximumcurrent level that can be delivered is regulated for each grid phase, inorder to support the grid as far as possible, on the one hand, withoutexposing components to the risk of damage, on the other hand.

A particularly preferred embodiment is one in which the wind turbine canbe operated by an external input that corresponds to the stipulationsmade by a distant control station. In this way, a power supply companyfor example can request the wind turbine to deliver the amount ofcurrent which is needed at that moment to support the grid.

Other advantageous embodiments of the invention are described in thesubclaims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

One embodiment of the invention shall now be described in detail withreference to the figures. These show:

FIG. 1 a wind turbine that feeds power to a grid, in a simplified view;

FIG. 2 a control device according to the invention for operating a windturbine; and

FIG. 3 a block diagram of the main components in the control andregulation arrangement.

DETAILED DESCRIPTION OF THE INVENTION

A wind turbine 2, shown in simplified form in FIG. 1, comprising a rotor4 is connected to an electric grid 6 that may be a public grid, forexample. Several electrical loads 8 are connected to the grid. Theelectrical generator of wind turbine 2, not shown in FIG. 1, is coupledto an electrical control and regulation arrangement 10 that firstlyrectifies the alternating current generated in the generator andsubsequently converts the current into an alternating current with afrequency corresponding to the grid frequency. Instead of a grid 6, asingle load could also be supplied with electrical energy by the windturbine 2. The control and regulation arrangement 10 has a regulatingdevice according to the invention.

FIG. 2 illustrates the regulating device according to the invention. Therotor 4, shown in simplified form, is coupled to a generator 12 thatprovides an amount of electrical power that depends on the wind speedand hence on the wind power. The alternating current produced in thegenerator 12 is initially rectified and subsequently converted into analternating current that has a frequency corresponding to the gridfrequency.

With the help of a current sensor (not shown), the amount of currentbeing fed into the grid 6 (FIG. 1) is detected. Said current is comparedat the same time with a predefined value I(max).

If the current fed into the grid 6 now exceeds the predefined maximumcurrent I(max), the power generated by the entire wind turbine (and/orits generator) is adjusted by the regulating device in such a way thatthe current delivered to the grid does not exceed the predefinedthreshold value I(max). In the event of a short circuit, said currentregulation can be accomplished, for example, by the wind turbinedelivering a significantly lower level of power output to the grid thanpreviously, while using elsewhere outside the grid the power thatconsequently is not fed to the grid, for example for a dumpload(resistance), or by feeding the power which is not fed to the grid tocapacitors or other interim storage devices. As soon as fullavailability of the grid is restored, delivery of the stored energy tothe grid can be resumed.

In this way, even when there is a short circuit in the grid, the windturbine can continue to deliver power to the grid and support the gridwithout the current exceeding the predefined threshold value as a resultof the short circuit.

FIG. 3 shows constituent parts of the control and regulation arrangement10 in FIG. 1. The control and regulation arrangement 10 includes arectifier 16, in which the alternating current produced by the generatoris rectified. An inverter 18 connected to the rectifier 16 converts thedirect current back into an alternating current with a frequencycorresponding to the grid frequency. This current is fed into the grid 6in three phases L1, L2 and L3. The inverter 18 is controlled with thehelp of a microcontroller 20 that forms part of the regulating device.The microprocessor 20 is coupled for this purpose to the inverter 18.The input variables for regulating the current with which the electricalpower provided by the wind turbine 2 is fed into the grid 6 are themomentary current and/or the momentary currents, the grid frequency, theelectrical power output P of the generator, the power factor cos φ andthe power gradient dP/dt. Regulation, pursuant to the invention, of thecurrent to be delivered to the grid is implemented in microprocessor 20.The current in each of phases L1, L2 and L3 is separately detected andthe respective levels are taken into account in the regulationarrangement pursuant to the invention.

If the measured current (level) I(actual) of a phase rises above apredetermined maximum current, the inverter 18 is controlled in such away that the current (level) falls below the predefined maximum currentI(max), with the electrical energy generated from wind energy and notdelivered to the grid being used elsewhere, for example by beingoutputted to a resistance (dumpload) or stored in an interim storagedevice (e.g., a capacitor or Ultracap).

The control system for the wind turbine can operate independently. Thewind turbine then detects a short circuit in the grid, for example bymonitoring the voltages of the separate grid phases and/or their phaseposition. If predefinable threshold values for voltages and/or phasedifferences are reached, the wind turbine recognizes a short circuit andoperates according to an algorithm provided for such a case.

Owing to the external access (22), it is possible, for example for thepower supply company to whose grid the wind turbine is connected, tointervene in the operation of the wind turbine and, for example, tomodify the amount of current to be delivered to the grid, the type ofcurrent (active current, reactive current) and/or the phase angle and/orphase position, etc. In this way, the power supply company can adjustprecisely those values (current, voltage, electrical power) in respectof the power to be delivered to the grid by the wind turbine thatcorrespond to the requirements of the network operator.

1. A method for operating a power system comprising: generatingelectrical power with an electrical generator of a wind powerinstallation driven by a rotor to output the electrical power to anelectrical grid; sensing an electrical current of the electrical poweroutputted to the electrical grid to detect a fault in the grid;maintaining connection of the wind power installation to the grid duringthe fault to continue to supply electrical current to the grid from thewind power installation during the fault; limiting the electricalcurrent delivered by the wind power installation to the grid during thefault to less than a selected amount; controlling the wind powerinstallation from a control station distant from the wind powerinstallation to remotely adjust the amount of electrical currentdelivered by the wind power installation to the grid during the fault;and resuming normal function of the wind power installation when thefault is no longer in the grid.
 2. The method of claim 1, furthercomprising: regulating the electrical power outputted by the generatorto a load in response to an amount of current outputted to the load. 3.The method of claim 1, wherein the electrical current is an alternatingcurrent with a predefinable frequency.
 4. The method of claim 3, whereinthe predefinable frequency is substantially equal to a frequency of thegrid.
 5. The method of claim 1, wherein the outputted power does notexceed a predefinable amount, has a predefinable phase position andincludes a predefinable proportion of reactive current.
 6. The method ofclaim 5, wherein the power system is a multiphase system and phaseposition and a proportion of reactive current for each phase do notexceed a predefinable value.
 7. The method of claim 6, wherein for eachphase a value independent of other phases can be predefined.
 8. Themethod of claim 1, wherein the electrical current is limited for everyphase affected by a short circuit to a momentary value at a moment theshort circuit occurs.
 9. The method of claim 1 wherein the faultcorresponds to a grid voltage reaching a value that deviates by morethan 20% from a reference value.
 10. The method of claim 1 wherein thefault is a short circuit.
 11. The method of claim 1, further comprising:limiting the electrical power outputted to the electrical grid to atleast a predefinable amount of electrical power.
 12. The method of claim1, further comprising: limiting the electrical power outputted to theelectrical grid to at least a predefinable phase position.
 13. Themethod of claim 1, further comprising: limiting the electrical poweroutputted to the electrical grid to at least a predefinable proportionof reactive current.
 14. The method of claim 1 wherein the fault is agrid voltage fault.
 15. The method of claim 1 wherein the fault is aphase position fault.
 16. A power system, comprising: a wind powerinstallation including: an electrical generator coupled to a rotor tooutput electrical power to an electrical grid; a sensor operable todetect a fault in the grid; a regulating device configured to maintainconnection of the wind power installation to the grid during the faultand to continue to supply a limited current from the wind powerinstallation to the grid during the fault; and an external commandinput; and a control station remote from the wind power installationoperable to adjust the limited current during the fault by commandsgiven to the external command input of the wind power installation. 17.The power system of claim 16, wherein the regulating device of the windpower installation includes: a microprocessor operable to compare asensed electrical current outputted to the grid with a selected currentvalue.
 18. The power system of claim 16 wherein the external commandinput transfers data to the regulating device.
 19. The power system ofclaim 16 wherein the sensor of the wind power installation includes: adevice to detect a short circuit in the grid.
 20. The power system ofclaim 19 wherein the sensor of the wind power installation comprises: avoltage sensing device to detect a voltage of at least one phase in thegrid.
 21. The power system of claim 19 wherein the sensor of the windpower installation comprises: a phase monitor to detect a phase positionof currents and voltages of at least one phase in the grid.
 22. Thepower system of claim 16 wherein the fault is a short circuit, andwherein the electrical generator remains connected to the grid when theshort circuit occurs.
 23. The power system of claim 18, wherein: controlsignals are received via the external command input from a gridoperator, and in response to said control signals from the grid operatorthe wind power installation is controlled in response to needs of thegrid operator and hence that electrical power, including a non-reactivepower, a wind power, a current position, a voltage position or a phaseposition, is fed into the grid in a form as required by the gridoperator.
 24. The power system of claim 16, wherein the faultcorresponds to a grid voltage reaching a value that deviates by morethan 20%.
 25. The power system of claim 16 wherein the wherein the faultis a short circuit.
 26. The power system of claim 16 wherein the windpower installation remains connected to the grid when a grid voltagereaches a value that deviates by more than 20% from a reference value.27. The power system of claim 16 wherein the wind power installationremains connected to the grid when a grid voltage reaches a value thatdeviates by more than 40% from a reference value.
 28. The power systemof claim 16, comprising: a rectifier coupled to the generator andoperable to rectify alternating current (AC) power produced by thegenerator to direct current (DC) power; and an inverter coupled betweenthe rectifier and the grid and operable to convert the DC power to ACpower with a frequency corresponding to a grid frequency.
 29. The powersystem of claim 28, comprising: a microprocessor operable to control atleast the inverter, wherein the inverter is controlled so that at leastthe electrical current of the electrical power output to the electricalgrid does not exceed a selected value.
 30. A method for operating a windturbine comprising: generating electrical power from a generator coupledto a rotor and driven by wind; outputting the electrical power from thewind turbine to an electrical grid; detecting a fault in the electricalgrid based upon a sensed parameter; and regulating the electrical poweroutput to the electrical grid such that at least an electrical currentof the electrical power output to the electrical grid does not exceed aselected amount, and such that the wind turbine remains operable andconnected to the electrical grid so that the electrical power is outputto the electrical grid during the fault; controlling the amount of powersupplied by the wind turbine to the grid by commands submitted to anexternal command input of the wind power turbine from a control centerremote from the wind power turbine; and resuming normal function of thewind turbine when the fault is no longer on the grid.
 31. The method ofclaim 30, wherein the sensed parameter is a grid voltage.
 32. The methodof claim 30, wherein the sensed parameter is a phase position of a phaseof the grid.
 33. The method of claim 30, further comprising: sensing agrid voltage deviation of more than 20% from a reference value todetermine the occurrence of the substantial disruption.
 34. The methodof claim 30, further comprising: sensing a grid voltage deviation ofmore than 40% from a reference value to determine the occurrence of thesubstantial disruption.
 35. The method of claim 30, further comprising:sensing an electrical current of the electrical power output to theelectrical grid such that regulating the electrical power is based uponthe sensed electrical current.
 36. The method of claim 30, furthercomprising: sensing a grid frequency of the electrical power output tothe electrical grid such that regulating the electrical power is basedupon the sensed grid frequency.
 37. The method of claim 30 furthercomprising: sensing an amount of the electrical power output to theelectrical grid such that regulating the electrical power is based uponthe sensed power amount.
 38. The method of claim 30, further comprising:sensing a power gradient of the electrical power output to theelectrical grid such that regulating the electrical power is based uponthe sensed power gradient.
 39. The method of claim 30, furthercomprising: sensing a power factor of the electrical power output to theelectrical grid such that regulating the electrical power is based uponthe sensed power factor.
 40. The method of claim 30, further comprising:rectifying an alternating current (AC) power produced by the generatorof the wind turbine to direct current (DC) power; converting the DCpower to AC power with a frequency corresponding to a grid frequency;and monitoring a parameter associated with the AC power output to thegrid such that at least the electrical current of the generator does notexceed a selected generator current value during the fault.
 41. Themethod of claim 30, further comprising: sensing a short circuit on thegrid to determine occurrence of the fault.